For many work vehicles, such as skid steer loaders, it is important to provide operators some type of feedback to maximize productivity and to allow for effective control of the vehicle. Typically, the feedback is associated with the operating state of the vehicle and/or the operating/environmental conditions within which the vehicle is being operated. This feedback may be in the form of engine sounds, hydraulic sounds and/or various other forms. For example, one type of feedback that has typically been provided to operators derives from the change in force required to move pilot joysticks (referred to herein as hydraulically-linked joysticks) across the joystick position at which the vehicle begins to start/stop motion. By providing an indication of the initiation or termination of vehicle movement, such feedback allows an operator to precisely control the operation of the work vehicle.
For a conventional hydraulically-linked joystick, the force required to move the joystick generally corresponds to the sum of two different forces. The first force derives from the spring coupled to the joystick and is directly proportional to the magnitude of the movement of the joystick. Specifically, a single spring is typically coupled to the joystick that is configured to apply a linearly increasing spring force as the joystick is moved from its neutral position towards its full stroke position. The second force acting on the joystick is related to the hydraulic pressure within the system, namely the pilot pressure for the joystick and the downstream pressure controlled by the joystick. Since the hydraulic pressure within the system increases/decreases significantly at the point at which the vehicle starts/stops motion, this second force forms the basis for providing the desired operator feedback.
For example, FIG. 1 illustrates a graph charting joystick force or torque (y-axis) versus joystick angular position (x-axis) for a conventional hydraulically-linked joystick. Curve 600 charts the joystick torque deriving from the hydraulic pressure within the system and curve 602 charts the sum of the joystick torques (i.e., the sum of the torques deriving from the spring and pressure forces). As shown, an initial region 604 exists at which the torque changes as the spring is engaged/disengaged and the hydraulic pressure varies. Beyond this initial region 604, the joystick torque increases linearly as the joystick is moved towards the joystick position at which vehicle motion starts/stops (indicated by line 200). As shown in FIG. 1, at the start/stop position 200, the joystick torque deriving from the hydraulic pressure changes significantly (indicated by bracket 606), thereby providing for a substantial increase/decrease in the overall torque required to move the joystick across the start/stop position 200. This change in torque allows for the operator to easily identify the start/stop position 200 when operating the work vehicle.
With modern electro-hydraulic (EH) control systems, conventional hydraulically-linked joysticks have been replaced by electronic joysticks that substitute electrical connections for the hydraulic connections. Accordingly, due to the decoupling of the hydraulic pressure, current electronic joysticks lack the force-related feedback provided by conventional hydraulically-linked joysticks. For example, FIG. 2 illustrates a graph charting joystick torque (y-axis) versus joystick angular position (x-axis) for a typical electronic joystick. As shown, curve 608 includes a very short, initial region 610 at which the force initially increases/decreases. Thereafter, the joystick force increases/decreases linearly with movement of the joystick. Thus, the operator is not provided any feedback as to when the joystick is about to be moved across the start/stop position 200. As a result, with electronic joysticks, operators have lost the ability to “feel” the start/stop point 200 of a work vehicle's motion, which significantly inhibits the controllability of the vehicle (particularly with respect to performing tasks that require precise vehicle control, such as maneuvering through tight spaces).
Accordingly, a joystick configuration that provides for enhanced operator feedback when using an electronic joystick would be welcomed in the technology.